1. Field of the Invention
This invention relates generally to the field of plastic container manufacturing and tooling, and more specifically to processes and mold assemblies for making a plastic container having a deeper grip recess than was conventionally possible.
2. Description of the Related Technology
Plastic containers are typically fabricated using either injection molding or one of two types of blow molding. The blow molding process is characterized by using internal pressure to force a hot, soft plastic preform or parison against a molding surface. Blow molding can be performed using either a reheat stretch blow molding process, which is typical for plastic containers that are fabricated from polyethylene terephthalate (PET), or an extrusion blow molding process, which is typical for containers that are fabricated from such materials as high-density polyethylene and polyolefins.
In the extrusion blow molding process, a molten tube or parison is continuously extruded from an extrusion fixture. A mold assembly that moves at a speed that is substantially equal to the speed of the extruded parison periodically captures portions of the parison, and pressurization is applied to inflate the captured portion of the parison against the interior surfaces of the mold assembly. The mold assembly is typically mounted for motion on either a molding wheel, which moves in a circular path, or on a shuttle, which moves the mold assembly on a substantially straight path.
In either type of blow molding process, the hot formable plastic material begins to cool and harden as soon as it contacts the mold surface. However, to the extent that the shape defined by the internal surfaces of the mold deviates from a cylinder that is equidistant from the longitudinal axis of the parison or preform the formable plastic material will contact some portions of the internal mold surface before others. In cases where the container body is designed to have deep recesses such as grip recesses for receiving a consumers fingers, prominent projections are formed within the mold that the formable plastic material must contact and stretch around in order to reach the portions of mold surface that form the outermost portions of the container sidewall. The friction that is created between the expanding tube of hot, formable plastic material and such internal mold projections has created practical design limitations that have prevented container manufacturers from introducing designs that would otherwise be favorably received by the public.
A need exists for a method of manufacturing a plastic container that permits the formation of a container having features that are deeper and a result of greater stretching of the hot formable plastic material that has been conventionally possible. Moreover, a need exists for a mold assembly that permits container features that are deeper and more extreme than were previously conventionally possible to be molded.